Medical devices may be coated so that the surfaces of such devices have desired properties or effects. For example, it may be useful to coat medical devices to provide for the localized delivery of therapeutic agents to target locations within the body, such as to treat localized disease (e.g., heart disease) or occluded body lumens. Localized drug delivery may avoid some of the problems of systemic drug administration, which may be accompanied by unwanted effects on parts of the body which are not to be treated. Additionally, treatment of the afflicted part of the body may require a high concentration of therapeutic agent that may not be achievable by systemic administration. Localized drug delivery may be achieved, for example, by coating balloon catheters, stents and the like with the therapeutic agent to be locally delivered. The coating on medical devices may provide for controlled release, which may include long-term or sustained release, of a bioactive material.
Aside from facilitating localized drug delivery, medical devices may be coated with materials to provide beneficial surface properties. For example, medical devices are often coated with radiopaque materials to allow for fluoroscopic visualization while placed in the body. It is also useful to coat certain devices to achieve enhanced biocompatibility and to improve surface properties such as lubriciousness.
Coatings have been applied to medical devices by processes such as dipping, spraying, vapor deposition, plasma polymerization, spin-coating and electrodeposition. Although these processes have been used to produce satisfactory coatings, they have numerous, associated potential drawbacks. For example, it may be difficult to achieve coatings of uniform thicknesses, both on individual parts and on batches of parts. Further, many conventional processes require multiple coating steps or stages for the application of a second coating material, or may require drying between coating steps or after the final coating step.
The spray-coating method has been used because of its excellent features, e.g., good efficiency and control over the amount or thickness of coating. However, conventional spray-coating methods, which may be implemented with a device such as an airbrush, have drawbacks. For example, when a medical device has a structure such that a portion of the device obstructs sprayed droplets from reaching another portion of the device, then the coating becomes uneven. Specifically, when a spray-coating is employed to coat a stent having a tube-like structure with openings, such as stents described in U.S. Pat. Nos. 4,655,771 and 4,954,126 to Wallsten, the coating on the inner wall of the tube-like structure may tend to be thinner than that applied to the outer wall of the tube-like structure. Hence, conventional spraying methods may tend to produce coated stents with coatings that are not uniform. Furthermore, conventional spraying methods are inefficient. In particular, generally only 5% of the coating solution that is sprayed to coat the medical device is actually deposited on the surface of the medical device. The majority of the sprayed coating solution may therefore be wasted.
In addition to the spray coating and spin-dipping methods, the electrostatic deposition method has been suggested for coating medical devices. For example, U.S. Pat. Nos. 5,824,049 and 6,096,070 to Ragheb et al. mention the use of electrostatic deposition to coat a medical device with a bioactive material. In the conventional electrodeposition or electrostatic spraying method, a surface of the medical device is electrically grounded and a gas may be used to atomize the coating solution into droplets. The droplets are then electrically charged using, for example, corona discharge, i.e., the atomized droplets are electrically charged by passing through a corona field. Since the droplets are charged, when they are applied to the surface of the medical device, they will be attracted to the surface since it is grounded.
Conventionally, stents are coated using a nozzle to apply a solution containing a polymer and drug. The stent is held as it is moved in front of the spray nozzle by a fixture called a cross-wire that is comprised of fine wires which make contact with the stent struts.
Loading a stent on a conventional cross-wire fixture may be a complicated process, and there are various opportunities for errors in the loading process. The process steps for loading a stent on a conventional cross-wire fixture may include: loading a stent onto a cross-wire fixture; loading the cross-wire fixture with the stent into a multi-sprayer collar; and placing the assembly in a vertical alignment system and aligning it.
The existing means of mounting conventional stents for a spray coating process may include two tooling parts, namely an assembly cross-wire fixture and a production collar (also referred to as a multi-sprayer collet). This process involves a sensitive assembly and handling process. The nature of the design of the cross-wire fixture assembly means that the fixture may be strained beyond its elastic limit or the wire strained or broken during stent loading.
FIG. 1 shows conventional cross-wire fixture 100 and conventional collet 110. Conventional cross-wire fixture 100 includes end loop C frame 101, long C frame 102, and collet fixture C frame 103. Looped over end loop C frame 101 and collet fixture C frame 103 is cross-wire 140, which includes end loop of cross-wire 141 and collet-side loop of cross-wire 142. Specifically end loop of cross-wire 141 loops over end loop C frame 101, while collet-side loop of cross-wire 142 loops over collet fixture C frame 103. The central section of cross-wire 140 extends between end loop C frame 101 and collet fixture C frame 103 and is taut.
Conventional collet 110 of FIG. 1 includes frame fixture fitting 111, pick and place interface 112, and stem shaft 113. During the fixturing process, after the stent is placed on cross-wire 140, conventional cross-wire fixture 100 is inserted in conventional collet 110 by moving it in the direction of arrow 120.
FIG. 2.1 illustrates conventional cross-wire fixture 100 with cross-wire 140 correctly installed. FIGS. 2.2 to 2.5 depict some of the potential problems associated with conventional cross-wire fixture 100. Some inadequacies shown relate to the relationship between conventional cross-wire fixture 100 and cross-wire 140. FIG. 2.2 illustrates that, during installation, the fixture may be strained beyond its elastic limit. This results in a bent C frame, possibly causing the wire to be slack. Alternatively, the wire may be short, making it difficult to align the loaded stent, as shown in FIG. 2.3. The wire may be too long, making it difficult to tension and align the loaded stent, as shown in FIG. 2.4. The wire may be broken by the operator while manipulating the assembly, as shown in FIG. 2.5.
Another problem arises from the requirement that the fixture be fitted to the collar each time a new stent (or other medical device) is installed on the cross-wire. The fixture to collar fit may be incorrect due to the open-ended design of the fixture. The fixture may be installed in an incorrect orientation with respect to the collar, may not be installed completely in the collar slot, and/or may be bent or otherwise damaged during the installation in the collar. Additionally, the collar slot may become fouled or otherwise blocked or damaged causing the fixture to become unusable.
A stent or other device that is fixtured on a cross-wire frame may undergo various processes while fixtured, including pre-weighing, aligning, spraying, drying (by heating, blowing and/or a vacuum), post-weighing, and final inspection.
An insert molding process allows the integration of a metal (or other material) device with a plastic, polyurethane, or other injection molded material. The metal (or similar material) device may be precisely aligned with the mold of the injection molded material to create a uniform product. This process is used to make screwdrivers, phasetesters, and similar objects.
There is, therefore, a need for a simple, cost-effective device for fixturing a medical appliance or other device that facilitates coating of the devices. Each of the references cited herein is incorporated by reference herein for background information.